1. Field
One or more embodiments of the following description relate to an apparatus and method restoring signals corresponding to a frequency band of an input signal using signals corresponding to another frequency band of the input signal.
2. Description of the Related Art
Recently, audio contents are expressed and stored usually by being compressed using a coding scheme such as moving picture expert group (MPEG) audio layer 3 (MP3) and windows media audio (WMA). Such coding schemes use a psychoacoustic model representing audibility characteristics of a human in different frequency regions. Here, these conventional coding schemes may not code high frequency components, e.g., high frequencies that are almost inaudible to human ears, to prevent deterioration of sound quality while increasing coding efficiency. In addition, although the original sound source may not be compressed with a low bit rate, a high frequency band of the sound source may not be encoded at all due to a low sampling rate.
In this case, a signal of the high frequency band may need to be restored by a frequency band expansion scheme. Here, the expansion scheme merely shifts a signal of a low frequency band to the high frequency band along a frequency axis.
According to related arts, in this case, discontinuity may be generated at a cutoff frequency, which forms a boundary between the low frequency band and the high frequency band. Furthermore, when the signal of the low frequency band is simply frequency shifted to represent the signal of the high frequency band, because an original envelope for the high frequency band actually has different characteristics compared to an envelope for the low frequency band, an error may occur in the signal of the restored high frequency band.
Thus, low sound quality may be derived even after the signal of the high frequency band is restored.